SPD leader Andrea Nahles said she would use a roadmap with which to measure the progress of the ruling coalition, which has been plagued by infighting, at a mid-term review next year.
The CDU's General Secretary Annegret Kramp-Karrenbauer echoed Nahles' promises, stating that the coalition must identify "three concrete projects for the coming months that we implement". The SPD's Nahles has hastened to claim that "the state of the government is unacceptable". She didn't specify what they might be.
"The message to the parties ruling in Berlin is: People want fewer disputes and more focus on the important issues", he said.
Projections for ARD and ZDF public television, based on exit polls and partial counting, gave the CDU 27-28 per cent support and the centre-left Social Democrats almost 20 per cent.
In September a year ago, Merkel's CDU party won the general election but more than 13% of the voting population chose the right-wing nationalists AfD, which are anti-Islam and anti-refugee. That would be the worst result in the region for the Social Democrats since the Second World War.
There were gains for the Greens, who were roughly level with Social Democrats at almost 20 percent - compared with 11.1 percent five years ago. Meanwhile, the right-wing, anti-immigrant Alternative for Germany (AfD) tripled its vote share from 2013 and allowing it to enter parliament for the first time with 13.2% of the vote.
The Greens' strong performance in Hesse means Bouffier will likely be able to remain state premier at the helm of a CDU/Greens government.
A three-way coalition with the Greens and the pro-business Free Democrats was already on the cards before bedtime Sunday night. Back in 2013, the CDU had to make a coalition with the Alliance 90/The Greens after the election resulted in no clear victor.
The Greens, who have governed Hesse in coalition with the CDU over the last 5 years, were neck-and-neck with the SPD, also securing 19.8% of the vote.
The projections left uncertain whether Bouffier's outgoing coalition would keep its parliamentary majority, and exactly what other combinations might be possible. The state is home to 6.2 million of Germany's 82 million people.
While the internal battles in her government have mostly been sparked between the CDU and the more conservative CSU, the Social Democrats have ended up footing a costlier bill in lost votes.
The AfD, meanwhile, gained 12 percent of the votes.
German Chancellor Angela Merkel says she will not seek re-election as the head of her party, according to unnamed party sources.
German Chancellor Angela Merkel will quit as head of her Christian Democratic party after nearly two decades, a person familiar with the matter said, a dramatic sign of her waning authority that will raise questions about her staying power as chancellor. It has failed to convince voters that it's achieving much on other matters.
Backing for Merkel's coalition partner, the centre-left Social Democrats (SPD), also plummeted, falling from 31 per cent to 20 per cent - a low not seen in 72 years.